Former security tsar Zhou Yongkang voiced strong support for President Xi Jinping yesterday as he re-emerged on the public stage for the first time since being investigated for corruption in August.

Zhou, a retired member of the Communist Party's all-powerful Politburo Standing Committee, attracted attention with a visit to his alma mater, China University of Petroleum, which analysts suspect was aimed at countering the intense speculation about the graft investigations surrounding his family members and protégés.

The 70-year-old, who graduated in 1966 with a major in exploration, spent all morning on the campus, a university spokeswoman said in a phone interview. It celebrates its 60th anniversary today.

The university released at least 20 pictures on its website But the official reception was low-key compared to appearances by other retired leaders. Zhou was only accompanied by the university's president and party secretary and no senior Beijing official was mentioned in the university's press release. The visit was also not mentioned in any major state media.

Zhou gave Xi his full backing when meeting old classmates and school officials, urging them to pursue the "Chinese dream", a Xi catchphrase.

"[The university] should become a first-class research university and contribute to the building of a moderately prosperous society and write a new chapter of the petroleum sector [as part of the] Chinese dream," he was quoted as saying in a report on the university website.

He said teachers and students must uphold the unity and unification of the party headed by Xi, and urged students to follow the instructions of the president.

Chen Ziming , a Beijing-based political analyst, said the underreported appearance of Zhou showed opinions were divided among top authorities, but it was more likely that the investigation was continuing.

"Many of his protégés have been detained, and that's a telltale sign of the investigation of Zhou," Chen said. "We can't say Zhou's appearance indicates that the investigation is over, as Bo Xilai also showed up before his arrest."

Ex-Chongqing party secretary Bo, who was sentenced to life in prison last month, made a public defence days before his detention in March last year.

Authorities endorsed the decision to probe Zhou at the secretive annual party meeting in August at the Beidaihe resort, the Post reported earlier. No Politburo Standing Committee member - retired or sitting - has been investigated for economic crimes since the end of the Cultural Revolution in 1976.

Several of Zhou's former aides have been placed under party disciplinary investigation, including Jiang Jiemin , ex-chairman of China National Petroleum Corporation, and disgraced deputy Sichuan governor Guo Yongxiang.

This article appeared in the South China Morning Post print edition as Zhou seen in public amid speculation of graft probe